Double-difference seismic tomography was performed on travel time data from a carbon sequestration site at the Aneth oil field in southeast Utah as part of a Department of Energy initiative on monitoring, verification, and accounting (MVA) of sequestered CO2. A total of 1,211 seismic events were recorded from a borehole array consisting of 22 geophones. Most likely because of the poor geophone arrangement, a low-velocity zone in the Desert Creek reservoir can only be detected when voxels containing the highest ray path coverage are considered. MVA accuracy and precision could be improved through the use of a receiver array that provides more comprehensive ray path coverage. A synthetic analysis was performed to determine the effect of receiver arrangement on the success of passive seismic tomography as an MVA tool for varying CO2 plume sizes and locations. Seismic event locations were generated to represent induced seismicity from injection, and five geophone arrays were created to monitor this artificial seismicity. A quantitative comparison was made between each calculated velocity model and its corresponding synthetic model.

1. INTRODUCTION

Climate change is a significant international concern, often attributed to increasing concentrations of greenhouse gases, namely Carbon Dioxide (CO2), in Earth’s atmosphere. The burning of fossil fuels is the source of the majority of anthropogenic CO2 emissions, but also sustains the ever-increasing global power needs. One method for reducing the amount of CO2 released into the atmosphere is geologic carbon sequestration. Geologic carbon sequestration is the capture of CO2 before it reaches the atmosphere, and storage of the captured CO2 in deep geologic formations, such as depleted oil reserves, unmineable coal seams, and deep saline aquifers. It is important to monitor, verify, and account for CO2 during and after injection. One tool that can be used to perform this task is seismic tomography.

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